Question

Two neon lights are turned on at the same time. One blinks every 3 seconds and the other blinks every 7 seconds. In how many seconds will they blink at the same time?

Answer 1

Answer: 21 seconds

Explanation:

The multiples of three in order are:

3, 6, 9, 12, 15, 18, 21

The multiples of 7 in order are:

7, 14, 21

So the lights would blink at the same time in 21 seconds